1. Field of the Invention
The present invention relates to a molding structure for a flyback transformer, and in particular to an improved molding structure for a flyback transformer which is capable of easily molding a bobbin having coils wound thereon in the interior of a casing using an epoxy resin, etc.
2. Description of the Conventional Art
As shown in FIG. 1, in the bobbin structure of a conventional flyback transformer, a plurality of ribs 3 are co-centrally protruded from an outer circumferential surface of a basic bobbin portion 1a at a predetermined interval.
A low voltage coil (hereinafter called a primary coil) 2 is wound on an outer surface of a basic bobbin portion la between the ribs 3.
In addition, a film guide 5 having a predetermined height which is higher than that of each rib 3 is formed at both ends of the basic bobbin portion 1a.
An insulation film 6 having a predetermined width corresponding to the longitudinal distance of the basic bobbin portion 1a is wound on the outer surfaces of the primary coil 2 and the ribs 3. A high voltage coil (hereinafter called a secondary coil) is wound on the upper surface of the insulation film 6.
At this time, more than one insulation film and secondary coil may be wound on the upper surface of the secondary coil 4, respectively.
As shown in FIG. 2, there are provided a ferrite core insertion member 13 having a core contact surface 14 formed in one side thereof and an insertion portion 11 formed in the center thereof. The ferrite core insertion member 13 is formed at an end portion of the bobbin 1, namely, on the upper end portion of the coil portion 10.
When a channel-shaped ferrite core 15, which is used for inducing a secondary voltage based on the primary voltage, is inserted into the ferrite core insertion portion 11 of the ferrite core insertion member 13, a recessed portion 15a of the core 15 contacts with the core contact surface 14.
In addition, as shown in FIG. 3, the coils 2 and 4 and the bobbin 1 are inserted into the casing 20 in order to enable an insulation and to prevent a leakage and discharge of a high voltage, and the casing 20 and the portion between the coils and bobbin (namely, a casing space portion) are molded using an epoxy resin, etc. A lead connection portion 17b is formed at one end (namely, at the opposite portion of the portion in which the ferrite core insertion member 13 is formed) of the casing 20 into which the bobbin 1 is inserted.
A high voltage lead 17 is connected with a high voltage terminal 17a formed in the interior of the bobbin 1 and is inserted into the lead connection portion 17b for supplying a high voltage of an anode to the Braun tube.
At this time, when molding the casing space portion using the epoxy resin 19, a rubber bushing 18 tightly contacting with the high voltage lead 17 is engaged to the upper portion of the lead connection portion 17b, into which the high voltage lead 17 is inserted, in a shape that the upper portion of the lead connection portion 17b is surrounded so that the epoxy resin 19 is not leaked to the outside of the casing 20 in the interior of the lead connection portion 17b.
After the molding operation is completed, as shown in FIG. 2, the ferrite core 15 is engaged to the ferrite core insertion member 13 for thereby fabricating a flyback transformer.
In the drawings, reference numeral 16 denotes a resin which is leaked to the outside.
However, when fabricating the conventional flyback transformer, the casing space portion is molded using the epoxy resin, etc. Therefore, a predetermined gas and gas bubbles are generated due to a high temperature molding operation, so that the epoxy resin is not uniformly formed in the space portion of the casing due to the gas and bubbles.
Namely, since the casing is sealed, the epoxy resin which is provided into the interior of the casing receives a repulsive force of the air in the interior of the casing. The above operation will be explained in more detail. For example, when inserting a piston into a cylinder, since there are not any holes for exhausting the air in the cylinder to the outside, a predetermined force is generated with respect to the supply of the epoxy resin in the cylinder. Therefore, the epoxy resin is not uniformly formed between the coils and the insulation film. Due to the above-described problems, it is impossible to enable a desired insulation between coils.
In addition, when a molding operation is performed using the epoxy resin, since the epoxy resin, which is overflown, is formed on the upper surface of the core contact surface, when the core is inserted into the bobbin, the thusly overflown resin contacts with the recessed portion, so that the ferrite core may not be installed at the normal position due to the height of the overflown resin, and the electric characteristic of the product may be changed. In addition to that, a predetermined problem may occur when engaging the core.
Furthermore, in order to prevent the epoxy resin from being leaked to the outside of the casing, since a rubber bushing is additionally used, the number of fabrication processes is increased. The rubber bushing may be extended during a high temperature process and may be escaped from the lead connection portion, so that the resin may be leaked to the outside.